Process of producing available phosphoric acid.



UNITED STATES PATENT orrion.

WALTER S. LANDIS, OF NIAGARA FALLS, ONTARIO, CANADA, ASSIGNOR TO AMERICAN CYANAMII) COMPANY, OF NASHVILLE, TENNESSEE, A CORPORATION OF MAINE.

PROCESS OF PRODUCING AVAILABLE PHOSPHORIC ACID.

No Drawing.

Specification of Letters Patent.

Application filed July 12, 1913.

Serial N 0. 778,730;

Niagara Falls, in the Province of Ontario and Dominion of Canada, have invented certain new and useful Improvements in Processes of Producing Available Phosph orioAcid; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to a process of rendering available, as a plant food, insoluble phosphates, and has for its object to provide a method which will be more expeditious as well as more efficient than those heretofore proposed.

\Vith these and other objects View, the invention consists in the novel steps constituting my process all as will be more fully hereinafter disclosed and particularly pointed out in the claims.

It is known when sodium sulfate Na,SO,,

or sodium carbonate Na-,CO is mixed withfinely ground phosphate rock, such as Tennessee or Florida rock, which contains phosphoric acid, in the form of a tricalcium phosphate, and the mixture then heated, that the phosphoric acid present is changed from the tricalcium form to a form which responds to the standard availability tests as proposed by the Official Association of rrgricultural Chemists. It is also well known that heretofore in order to bring about this transformation on a commercial scale, the mixture has usually been ground to a greater or less fineness, treated with water and heated in a rotary kiln or other device, until the conversion tookplace. But in all such cases it is equally well known that the efficiency of the conversion has been low and unsatisfactory, a large amount of the phosphate being discharged from the heating apparatus with, say, only half of the phosphate transformed, or when a high efficiency of conversion was obtained, the total output from the kiln was so low and the fuel consumption so high that the process as a whole ,was a commercial failure. this failure is largely due to the slow drying of the mixed materials in the kiln, which permits the sodium salt or salts to crystallize and therefore segregate so that the calresults,

I have discovered that the cause of.

cining process does not yield good results, all as Wlll presently appear.

In carrying out my process I take, for example, ground Tennessee phosphate rock or Florida pebble phosphate rock, or any other phosphate material, in which the phosphorus is present essentially in the form of a tricalcium phosphate, and mix the same with say 5% to 20% of sodium carbonate, or sodium sulfate, commonly known as salt cake or niter cake. I prefer to mix these materials dry in the proper proportions, and find about 10% sodium carbonate gives good or slightly more than 10% of sodium sulfate. I preferably grind them wetin a tube mill or any other similar fine inding device, and have found that the Eider the grinding the lower may be the temperature of the subsequent calcining operation, the shorter the duration of the said operation, and the lessthe quantity of the reagent required. A fineness permitting 85% to 90% of the mixture to pass through a 200 mesh screen, gives very satisfactory results. I find also that the amount of Water added plays a very important part in the subsequent chemical reaction that takes place in the kiln. In fact, this water of addition and its subsequent removal, constitutes an important portion of the novelty of my process, as will. appear below, for I have found it is conduclve to the best results in this process to add justenough water to make a saturated solution of the sodium salt. In other words; where there has been heretofore added 15% of sodium sulfate, it was found necessary to add from 30% to 40% of water to the weight of the dry mixture of ground phosphate rock, and sodium sulfate. The exact amount-depends somewhat upon the temperature of the mixed materials for, of course, the temperature influences the solubility of the sodium sulfate. But such a saturated solution, upon suffering a change of temperature, or being subjected to evaporation of its water, will immediately show evidences of crystallization of the sodium sulfate; and if these changes in temperatures are slow, or if the evaporation process is slow, the crystals grow very rapidly indeed. This, of course, causes a segregation of the sodium sulfate reagent, as above stated, as well as an uneven distribution; so

Patented Apr, 28, 19141.

that if such a mixture is put into a ro- 11o tary kiln, the results are extremely disappointing. Further, if a wet mixture of phosphate rock and sodium sulfate is charged into a long rotary kiln at a com mercial rate of feed, the consequent slow evaporation necessitated by such a kiln, seems to cause this crystallization to take place in the kiln itself, and the calcining of such a segregated mass therefore does'not yield'good results. On the other hand, it have discovered if a mixture of phosphate rock, sodium sulfate and water is prepared in the proportions of,for examplel00 parts phosphate rock, 12 parts sodium sulfate and 40 parts water, and dried quickly by being dropped and spread out w in a thin layer on avery hot surface, no

such crystallization and segregation as described above, will take place, and there will result from'such drying a dry porous mass of considerable strength, which may be fed to a rotary kiln at a very fast rate, while the resulting product out of the kiln will show 97% of the total phosphoric acid present as being in the available form,

To make the difierence between my proc ess. and the old process very clear, it is said :A 5'x40' kiln fed with wet. material directly will not produce over 600 lbs. to.

800 lbs. of a product per hour showing say 95% of the phosphoric acid available. llf,

however, the material is dried in the iii-- stantaneous manner above described, and the dry mass fed to the kiln, then the output ofthe same kiln will be from 5000 lbs. to 8000 lbs. of the same product per hour,

with a consequent lowering of the fuel consumption' of the kiln. Further, the subsequent calcination in the kiln offers no difli' culties" with a properly dried material, whereas it is practically impossible to get a uniform product without such drying. The

temperatures at which this calcination takes place in a kiln are between say 900 C. and although this will vary with the fineness of, grinding, the evenness of distribution of the reagent and the character of the phosphate rock employed, as certain impurities, like silica and lime in the rock, have a decided influence upon the necessary temperature for such calcination. v

It will now be clear that. an essential feature of my process, consists of a rapid preliminary drying ofthe mixture before heating the mass in the kiln, such drying serving to rapidl drive 0d the water, so that no segregation of soluble salts can take place, and no large crystals can be formed, whereby l maintain a perfectly uniform distribution of the reagent in the mixture, from the beginning of the process to the end.

resales? Of course ll do not wish to be restricted in any way to any particular type of drytory. For instance, a drier lined with a re fractory material, and so highly heated that the surface upon which the wet material falls is red hot at the time of impingement of the wet mass operates well, and especially if the mass is fed in a thin layer on such highly heated surface, so that the drying will be almost instantaneous. It is also desirable to finely divide the mixture after calcining, but this is only necessary to develop its highest availability. What I claim is v 1. The process of treating phosphatic material in order to render insoluble phosphates available which consists in prepar-- ing a finely divided mixture consisting of said material, a sodium salt and water; dry- 1 g salt to crystallize to a substantial extent; and then calcining the dried mixture to rendersoluble the contained phosphates, substan tially as described. 2. The process ofchanging insoluble phosphates into the soluble form which consists in preparing a finely divided mixture of tricalcium phosphate material, a sodium salt and water; drying said mixture so rapidly said mixture withoutv permitting said 'ing apparatus, but a very highly heated rotating cylindrical drier is found satisfacthat no substantial crystallization of a conble form which consists in finely dividing said rock; mixing sodium sulfate therewith; treating the mixture with water; drying the wet mixture thus produced so quickly as to prevent said sodium sulfate from crystallining to an appreciable extent; and finallycalcining said dried mixture at a temperature sufficient to produce the desired change, sub-,

stantially as described.

4. The herein new composition of matter suitable for calcining consisting of a thor oughly dried mixture of divided phosphate rock and a soluble sodium salt substantially free from soluble crystals, substantially as described.

In testimony whereof I affix my signature in presence of two witnesses.

warren s. mums.

Witnesses: S. TTANNA, I 7

J. L. Down. 

